Examples of viologen-based systems are described in patents U.S. Pat. No. 5,239,406 and EP-612 826.
Electrochromic systems have been very widely studied. They generally comprise, in a known manner, two layers of electrochromic materials separated by an electrolyte and framed by two electrodes. Under the effect of an electrical power supply, each of the electrochromic layers may reversibly inject cations, which leads to a modification of its properties (for example, for tungsten oxide, a change in color from a pale blue to a dark blue).
The most promising electrochromic systems are the “all-solid” systems, that is to say those whose layers, and particularly the electrolyte, are all of an essentially mineral nature: in fact it is possible to deposit all the layers successively on the same substrate, by the same type of technique, in particular sputtering. Examples of these all-solid systems are detailed in patents EP-867 752, EP-831 360, WO 00/03289 and WO 00/57243.
There are also other electrochromic systems, in particular those where the electrolyte is a polymer-based or a gel-based layer, the other layers generally being mineral (reference may be made, for example, to patents EP-253 713 and EP-670 346).
There are also other electrochromic systems where all the layers are polymer-based, these are then referred to as “all-polymer” systems.
The invention relates in particular to the “all-solid” electrochromic systems.
Many applications have already been envisioned for these systems. Most generally, this has involved employing them as glazing for the building industry or as glazing for a vehicle, in particular as sunroofs, or else as anti-dazzle rear-view mirrors, then operating in reflection rather than in transmission.
Other applications can now be envisioned, which require the juxtaposition of a plurality of electrochromic systems, most particularly in order to use them as display means or in order to darken a glazed electrochromic surface only locally (for example to counter local glare). It is therefore desirable to have a greater degree of freedom in the way in which an electrochromic system is able to darken, and it is sought to be able to control this optical/energy change locally and selectively.
It will be sought to alter the energy properties of the system when aiming for thermal comfort inside a passenger compartment or a building. It wilt be sought to alter the optical properties when improvement of visual comfort is involved or when a display device is involved.
Patent application WO 98/29781 discloses an electrochromic system broken down into regions which can be selectively activated. The electrical power supply to each of these regions has not, however, been studied in detail.
Patent application WO 98/08137 also discloses a glazing called chromogenic glazing, consisting of the juxtaposition of two chromogenic systems. These two systems are assembled, in particular to form a vehicle sunroof, effectively having two regions the color level of which can be modified one independently of the other.